Thermostatic switch



June 16, 1942. G. s. BRAUN 2,286,459

THERMOSTATIC SWITCH Filed Nov. 10, 1941 @wz'fym J filazzzz ff 541/1 W 4 2 orzzgy Patented June 16, 1942 THERMOSTATIC SWITCH Gwilym S. Braun, Strasburg, Ohio, assignor to Knapp-Monarch Company, St. Louis, Mo., a corporation of Missouri Application November 10, 1941, Serial No. 418,454

6 Claims.

My invention relates to thermostatic controls and particularly controls designed to shut off an electric current when a device to which they are applied reaches a predetermined heated condition,

Among the objects of my invention is to provide a new and improved thermostat control wherein the parts are relatively few and simple and wherein the steps required to assemble the control are reduced substantially to a minimum.

Another object of my invention is to provide a new and improved type of thermostatic control wherein the thermostatic element is entirely loose and so positioned within a retaining block that when subjected to heat the entire force of expanding bimetal will be exerted against a switch which is designed to be opened by it under heated conditions.

Still another object of my invention is to provide a new and improved thermostatic switch construction wherein a block of electric insulating material is so provided with a slot for reception of a loose bimetallic element, the depth of which can be varied during molding either to accommodate bimetallic strips of different thickness and sensitivity or which can be varied so that the temperature at whichlthe bimetallic strip becomes effective can be varied by reason of a resilient movable switch arm being located at varying distances from the position of the bimetallic strip.

The object of my invention primarily is to provide a new and improved switch which is inexpensive in construction by reason of the fact that the major portion of the mounting is a molded ceramic block on which metallic parts have been reduced in number and size, thereby reducing the cost of metal incorporated into the device.

With these and other objects in view, my invention consists in the construction, arrange ment and combination of the various parts of my device whereby the objects contemplated are attained, as hereinafter more fully set forth,

pointed out in my claims and illustrated in the accompanying drawing, in which:

Figure 1 is a plan view of a flatiron illustrating the installation of my new and improved thermostatic control.

Figure 2 is a plan view of the control alone L Figure 4 is a cross sectional view taken on the line 4-4 of Figure 3.

While it is old in the art to provide thermostatic controls for electric appliances and particularly for toasters, wafile irons, flatirons and the like, the controls have customarily been made adjustable or at least operative at rather carefully selected temperatures. In order to accomplish results of this kind, the controls have had to be designed and built with considerable precision limiting tolerances and necessitating a large number of operations in manufacture and assembly. By reason of the fact that slight increases in the manufacturing cost cause rather large increases in the retail price to the consumer because of these devices passing through many hands before the retail sale is made, it has become highly essential to keep the cost of manufacture as low as possible in order to provide appliances equipped with the necessary safety controls which are within a price range which can be purchased by the average individual. The design of appliance incorporating my invention emphasizes primarily the safety feature which prevents the appliance from becoming overheated though the operator might be negligent about turning the heating current on and off.

In the embodiment selected to illustrate the application of my thermostatic control to an electric appliance, there is shown a sole plate ID of a flatiron provided with a recess I! for the reception of a resistance wire l4 embedded in a suit-able matrix Hi, the matrix in the recess being covered by a plate I8. The plate, as shown in Figure 1, is secured to the sole plate by means of rivets 20. One end of the resistance wire is shown at 22 and the other end at 24, both being insulated from the plate l8 by means of porcelain insulators 26.

The thermostatic control proper consists of a block 30 preferably of some ceramic material which is effective as an insulator against electricity but which will readily pass heat from the appliance into the thermostatic control. In the block there is formed an elongated recess 32 and adjacent one end of the recess is an aperture 34 and at the other end an aperture 36. Both of the apertures are enlarged at the ends adjacent the face of the block which is normally in contact with the plate l8. Another aperture 38 at one side of the block is adapted to receive a screw 40 for attaching the block to the plate [8. In

- order to prevent rotation of the block from its proper position on the plate, the enlarged portion of the aperture 34 may be extended or an additional recess or pocket provided in order to locate the block over one of the rivets Ill.

It will be noted that the upper surface 42 of v the block adjacent the aperture I8, as shown in Figure 3, is sloped inwardly toward the recess 32. A movable switch arm 44 extends over the apertures l4 and SI and spans the recess". The movable switch arm has also an end 48 extending beyond the outside wall of the block to which one wire 24 of the resistance coil may be attached by means of a bindingpost 48, as shown in Fig- 'ure '1. The movable switch arm is secured to the block by means of an eyelet II which presses the switch arm against the sloping surface 42. At the other end of the block an eyelet I2 secures a terminal I4 to the block. The terminal,

as indicated inFigure 2, has an electric wire it permanently attached thereto at the upper side It, as shown in Figure 2. It will also be noted that the top of the eyelet 52 is positioned at approximately the same level as the upper side of the eyelet 50. By being so positioned, the free end of the movable switch arm 44 which rests i upon it is elevated'above the position itwould normally take due to it being depressed by the sloping character of the surface 42. Positioned as shown, the central portion of the switch arm is normally under tension and bent slightly as shown by the full lines in Figure 3. The top of the eyelet 52 forms a fixed switch point for the thermostatic control. I

A bimetallic strip 60 is shown loosely positioned ously pressed against the bottom of the recess 32. As the temperature continues to rise, a point is reached where the bimetallic strip exerts force enough to lift the movable switch arm 44 out of contact with the fixed switch point 54, thereby breaking the circuit through the resistance wire. Continued heating of the appliance will thereupon become arrested until the bimetallic strip cools ofl. sufliciently to'permit contact to be made again between the switchpoints.

There has thus been provided a thermostatic control wherein an electric insulating block provides the major portion of the construction necessary to house a bimetallic element and attach suitable electric switch members thereto in order to provide a simple construction-for the control.

Some changes may be made in the construcance comprising a block of electric insulating material having heat conducting properties adapted to be attached adjacent a heated portion of the appliance, said block having an elongated recess therein, a resilient movable switch arm exin the bottom of the recess 32. The strip, as best contact with the arm.

In the design'of the block which is customarily made by amolding process, the depth ofthe recess 32 can be varied by adjustment of a suitable block in the molding die. By varying the depth of the recess 32- a greater or less amount of clearance can be provided between the lower surface of the movable switch arm 44 and the bimetallic strip. -Moreover, if desired, the thickness of the bimetallic strip 80 can be varied so that the strip will be effective at correspondingly varied temperature conditions. By reason of the fact that the dimensions of the block 30 and recess 32 can be very carefully controlled and regulated in the molding process and by reason of the fact that the thickness of the bimetallic strip can be carefully selected, an inherent accuracy is built into the thermostatic switch making-it unnecessary to carefully check and regulate each device whichis manufactured.

In operation, the bimetallic strip 60, when cold or in normal position, lies flat in the bottom of the recess 32. Likewise under normal conditions before the current is applied, the resilient movable switch arm so that it is in fact out of close v ble switch arm 44 is under tension; tending to be pressed down against the fixed switch point 54.

When electriccurrent is applied tothe resistance wire i4, the sole plate of the fiatiron becomes heated and heat gradually spreads to the plate It and the block 30. As the block becomes heated, the bimetallic strip becomes heated and both endsbegin to curve upwardly to the dotted line position as shown in Figure 3. The

tending over said recess and over the block beyond the ends of the recess, a connection adja-' cent one endof the recess securing the switch arm at one end to the top of the block, a connection at the other end of the recess having an. electric terminal attached thereto comprising a fixed switch point normally in contact with a free end of the switch arm and supporting said free end in a position displaced from the natural free position of the arm whereby the central portion of said arm is normally under tension, and a bimetallic strip 1y g in normal position loosely in the bottom of "the recess and having aposition when subjected to excessively high temperatures wherein the central portion is bowed against thebottom of the recess and both ends thereof are extended outward against the resilient switch arm at spaced intervals elevating the free end of the arm out of contact with the fixed switch point.

2. A thermostat control for an electric appliance comprising a block of electric insulating material having heat conducting properties adapted to be attached adjacent a heated portion of the appliance, said block having an elongated recess therein and an aperture in the block adjacent each end of the recess, a resilient movable switch arm extending over said apertures and the recess, a connection attaching a portion of said switch arm overlying one of said apertures to the block, a connection at the other aperture having an electric terminal attached thereto comprising a fixed switch point normally in contact with a free end of the switch arm and supporting said free end in a position slightly elevated from the natural free position of said arm wh'ereby thecentral portion of said arm is normally depressed under tension, and a bimetallic strip of selected sensitivity lying in normal position loosely in the bottom of the recess and having a position when subjected to excessively high temperatures wherein the central portion is bowed against the bottom of the recess Q 7 midportion' of the bimetallic strip is simultane- 76 and both ends thereof are curved upward against the resilient switch arm elevating the free end of the arm out of contact with the fixed switch point.

3. A thermostat control for an electric appliance comprising a block of electric insulating material having heat conducting properties adapted to be attached adjacent a heated portion of the appliance, said block having an elongated recess therein of predetermined depth and an aperture extending through the block adjacent each end of the recess, a resilient movable switch arm extending over said apertures and the recess, an eyelet extending jointly through one of said apertures and the overlying portion of said switch arm securing the arm to the block, an eyelct in the other aperture having an electric terminal attached thereto comprising a fixed switch point normally in contact with a free end of the switch arm and supporting said free end in a position slightly elevated from the natural free position of said arm whereby the central portion .of said arm is normally depressed under tension, and a bimetallic strip of selected thickness and sensitivity corresponding to the depth of said recess lying in normal position loosely in the bottom of the recess and having a position when subjected to excessively high temperatures wherein the central portion'is bowed against the bottom of the recess and both ends thereof are curved upward against the resilient switch arm elevating the free end of the arm out of contact with the fixed switch point.

4. A thermostat control for an electric appliance comprising a block of electric insulating material having heat conducting properties adapted to be attached adjacent a heated portion of the appliance, said block having an elongated recess therein of predetermined depth forming a pocket open on one side only and an aperture extending through the block adjacent each end of the recess, the portion of the block at the top of one of said apertures having a slope inward toward the recess, a resilient movable switch arm extending over said apertures and the recess, an eyelet extending jointly through the aperture having the sloping top and the overlying portion of said switch arm securing the arm to the sloping top in position tilted relative to the top of the block, an eyelet in the other aperture having a permanently wired electric terminal attached thereto comprising a fixed switch point normally in contact with a free end of the switch arm and supporting said free end in a position slightly elevated from the natural free position of said arm whereby the central portion of said arm is normally depressed under tension, and a bimetallic strip of selected thickness and sensitivity corresponding to the depth of said recess lying in normal position loosely in the bottom of the recess and having a position when subjected to excessively high temperatures wherein the central portion is bowed against the bottom of the recess and both ends thereof are curved upward against the resilient switch arm elevating the free end of the arm out of contact with the fixed switch point.

5. A thermostat control for an electric appliance comprising a block of electric insulating material, said block having an elongated recess therein, a resilient movable switch arm extending over said recess and over the block beyond the ends of the recess, a connection adjacent one end of the recess securing the switch arm at one end to the top of the block, a connection at the other end of the recess having an electric terminal attached thereto comprising a fixed switch point normally in contact with the free end of the switch arm and supporting said free end in a position displaced from the natural free position of the arm whereby the central portion of said arm is normally under tension, and a bimetallic strip in said recess having a position, when subjected to excessively high temperatures, wherein the central portion is bowed and whereby said strip engages said resilient switch arm to effect elevation of the free end thereof out of contact with said fixed switch point.

6. A thermostat control for an electric appliance comprising a block of electric insulating material adapted to be attached adjacent a heated portion of the appliance, said block having a recess therein and an aperture in the block adjacent each end of the recess, a resilient movable switch arm extending over said apertures and the recess, a connection attaching a portion of said arm overlying one of said apertures to the block, a connection at the other aperture having an electric terminal attached thereto comprising a fixed switch point normally in contact with the free end of the switch arm and supporting said free end in a position slightly elevated from the natural free position thereof whereby the central portion of said arm is normally depressed under tension, and a bimetallic strip of selected sensitivity lying in normal position in the bottom of the recess and having a bowed position when subjected to excessively high temperatures and thereupon engageable against said resilient switch arm to elevate the free end thereof out of contact with said fixed switch point.

GWILYM S. BRAUN. 

